Chemical derivatives of synthetic isoprene rubbers

Abstract

A process for cyclizing synthetic polyisoprene in the same way as natural rubber was developed to give a product which, for many applications, is equivalent to cyclized natural rubber.GR-S does not react under the same conditions.A process for chlorinating synthetic polyisoprene was developed which gives a product similar to chlorinated natural rubber with respect to chlorine content, viscosity, thermal stability, solubility, and general utility in protective coatings and rubber-to-metal adhesives.GR-S cannot be satisfactorily chlorinated under the same conditions.Synthetic polyisoprene readily adds hydrogen chloride in a manner similar to natural rubber, whereas GR-S is practically unaffected. The product, however, does not have the excellent film-forming properties of Pliofilm.The striking similarity in chemical behavior of synthetic polyisoprene and natural rubber is attributed to the common chemical structure.The relative chemical inertness of GR-S is attributed to lack of a methyl group attached to the double bond.ATURAL rubber was the subject of intensive investigation with respect to its chemical reactions and the preparation of commercially useful derivatives. General reviews in this field have been written by Fisher (11), Schidrowitz (87), Jones (17), Sibley (89), Memmler (84), Daw-son and Schidrowitz (7), and Farmer (9). Before World War II several of these reaction products, such as rubber hydrochloride (Pliofilm), isomerized rubber (Pliolite), and chlorinated rubber (Parlón), had been marketed successfully.During the past five years drastic restriction of the commercial use of natural rubber for chemical derivatives prompted the study of synthetic rubbers for this purpose. Endres (8) recentlyreported on chlorinated and cyclized synthetic rubbers, with special emphasis on GR-S as the starting material.This paper deals particularly with derivatives of polyisoprene and other isoprene-containing synthetic rubbers which behave chemically very much like natural rubber because of the similarity in structure. It is shown that GR-S and other butadienecontaining synthetic rubbers, under the same conditions, are either nonreactive or behave differently.Because of its similarity to the natural rubber product, isomerized synthetic polyisoprene' has been designated Pliolite S-l. Chlorinated synthetic poly-isoprene 4s referred to as Pliochlor. CYCLIZED ISOPRENE POLYMERSThe formation of rubber isomers by-reaction with halides of amphoteric metals, such as stannous and stannic chlorides, aluminum chloride, boron fluoride, and chlorostannic acid, was reported by Bruson, Sebrell, and Calvert (4). The properties of such derivatives which render them useful as molding materials were described by Thies and Clifford (33) and by Jones and Winkelmann (18). Properties of Pliolite-rubber mixtures were described by Thies (38). Thermoprenes, which are reaction INDUSTRIALAND ENGINEERING CHEMISTRY

Physical Properties of Diene Polymers - Effects of Side Vinyl Groups and Other Structural Features

“…Perbenzoic acid titration indicated a 1,4-addition content of 88%. Specific refraction from experimental values agreed well with the calculated value for polyisoprene (5). Chromic acid oxidation gave acetic acid corresponding to 89% of the theoretical content of 1,4-and 3,4-isoprene units.…”

The Reaction of Polyisoprene With Titanium Tetrachloride

“…Thus, Gordon (4)(5)(6), who studied the kinetics of cyclization of hevea latex, considered the reaction to involve the protonation of a double bond in cis-polyisoprene, followed by an attack of the-resulting carbonium ion on an adjacent double bond, both occurring in the Markownikoff sense, t o form a cyclic carbonium ion which then deprotonates to give structure I. Similar views were held by D'Ianni et al (2) and various other workers. Flory (11) calculated that if monocyclic rings are formed a definite proportion (13.5%) of the isoprene units should end up as "widows", i.e., not cyclized by virtue of their neighbors having already reacted, so that the final unsaturation of the completely cyclized rubber should be about 57y0 of that of the original rubber instead of the 50% unsaturation indicated by structure I.…”

“…Synthetic polyisoprenes also undergo cyclization quite readily ( 2 ) , but polybutadienes require fairly drastic conditions (3). This reaction has been considered for some time to involve a carbonium ion mechanism, although there is a controversy as to whether the product consists of monocyclic (2,(4)(5)(6)(7)(8) or polycyclic (3, 9, 10) ring structures. Thus, Gordon (4)(5)(6), who studied the kinetics of cyclization of hevea latex, considered the reaction to involve the protonation of a double bond in cis-polyisoprene, followed by an attack of the-resulting carbonium ion on an adjacent double bond, both occurring in the Markownikoff sense, t o form a cyclic carbonium ion which then deprotonates to give structure I.…”

Kinetics of Cyclization of Hevea Latex

“…When Hevea rubber, or under some conditions synthetic polyisoprene (11), is exposed to the action of heat (31) of a silent electric discharge (17), cathode rays (28), or acidic catalysts of the Lewis type (8) or Bronsted type (15), it is progressively resinified. The resin, like the parent rubber, has the empirical formula (C5H8)i.…”

“…may be calculated in a number of cases for the proton affinity of a C-C, if a substituent methyl group is replaced by hydrogen (IS). This should raise correspondingly the activation energy of cyclization and accounts for the great difficulty (11) of cyclizing butadiene polymers.…”